In the process for producing cement by mixing several kinds of material powder particles as raw materials for the cement, followed by adding water to the mixture, it has been known that the mixing state and the void fraction of the mixed material powder particles govern the density or the strength of the cement which has gelled. Specifically, it has been experimentally revealed that the strength of cement decreases as the void fraction of the cement increases, in other words, the strength of cement increases as the packing rate of the cement increases. In order to determine in what mixing proportion the material powder particles of cement should be mixed for the purpose of increasing the strength of the cement, or in what mixing proportion the material powder particles of cement should be mixed for the purpose of obtaining a desired strength, it is essential as the element technology to control the packing rate of mixed material powder particles in production.
Since the control of the mixing proportion of raw materials (material powder particles) for controlling the packing rate of powder has depended on empirical rules and intuition in the actual process, there are no measures to determine whether the selected mixing proportion is actually optimum or not. Furthermore, although raw materials change on a daily basis since waste materials are employed as raw materials for cement for the purpose of securing resources, it is necessary to employ such waste materials and constantly secure a cement property that gives a certain required strength. In order to obtain such a certain property, it is primarily important to control the packing rate of powder by selecting the proportion of raw material powder particles. In order to control the proportion of raw material powder particles so as to bring the packing rate within a certain range, the packing rate has been estimated by a skilled person's intuition based on his or her empirical rules, and thus, the cement has been produced so as to meet a certain level to some degree.